Regulating transformer



n- 1960 J. KREUZER ETAL 2,922,132

- REGULATING TRANSFORMER Filed July 21, 1955 s Sheets-Sheet 1 3 Sheets-Sheet 2 J. KREUZER El'AL REGULATING TRANSFORMER Jan. 19, 1960 Filed July 21, 1955 mm mm r n IN V EN T085 J. KREUZER ET AL- REGULATING TRANSFORMER Fild July 21, 1955 3 Sheets-Sheet 3 INVENTO S 41% W I @Jnmma United [States b 2,922,132 REGULA'IV'ING TRAV NsroRm: "R

The present invention relates to variable ratio transformers for supplying an alternating voltage which is adjustable to a desired value and particularly to. improvements in the connections of that part of the high voltage winding which is tapped. v I With transformers having a wide range of regulation it is customary to provide a separate coil for the formation of regulating steps which is hereafter referred to as regulating coil. This regulating coil extends over the entire length of the core leg and is comprised of a plu; reality of conductors wound helically. To avoid a disturbance of the ampere-turn distribution by 'steppings, which results in a decrease of the short circuit strength, the regulating coil is tapped only onits terminals. Consequently the regulating coil consists of so many strands as steps are provided. In many cases, for example with single phase transformers, it 'is desirable to divide the regulating coil in two parts which aredistributedon the two legs of a core-type. transformer orsurround the central leg of a shell-type transformer as concentric cylindrical coils. g t

The strands of the two parts of the regulating coil may be'connected in series or in parallel. Each ofsaid connections has its own characteristics which make it best suited for a particular field of application. 1 1

It is an object of this invention to combine the advantages of said connections'bypelirninating the disadvantages adhering to the usual series or parallel connect1on.

g It is a further object of the invention'to provide a regulating coil of the above-indicated character in which the ohmic losses in the connecting leads to thestageselector switch and the dynamic forces to which the connecting leads and their supports are subjected in the event of a short circuit, are considerably reduced.

It is also an object of the present invention to provide a regulating coil in which the currents flowing in the connecting leads to the stage-selector switch are compensated so that eddy currents in neighboring metal. parts caused by the resulting ampere-turns of the currents in the connecting leads to the stage-selector switch are avoided and also the influenceof such ampere-turns onthe shortcircuit voltage, which causes an uncertainty with regard to the value of the short-circuit voltage which the designer has to guarantee within small limits. 5

. The advantages of, the invention will-become apparent from the following description and the. accompanying drawings in which the regulating coil according to the invention will be compared with known embodimentsfof regulating coils to indicate the improvements obtainable therewith. The novel features .whichcharacterize our invention will be pointed out'inthe claims annexed to this specification. V

In the drawings:.

Fig. 1 is a circuit diagram of the knownseriesconnection of a regulating coil; I Fig. 2 is av circuit diagram Of the known parallelconnection of a regulating coil;

2,922,132 Patented Jam, 19, 1 960 Fig. 3 is a circuit diagramofLthe connection of a regulating coil according to the present invention.

In the drawings like reference characters indicate similar'parts in the different figures.

In the drawings, A and B are the magnetic corelegs on which there are wound the primary winding, the tapless part of the secondary winding (both for the sake of simplicity not shown) and the regulating coil consisting .of the winding sections C and C". The single strands of the winding sections C and C are series connected (Fig. l) or parallel connected (Fig. 2) by leads D and the terminals of each strand are led to the fixed contacts E --E of the ratio adjuster switch by conductors F. 1,to 8 are the terminals of each strand, terminals with the same potential having the same number. The sense of winding of each winding part CC" is indicated by arrows G. The direction of currents at a certain moment and under the assumption that all stages are in service is indicated by arrows H. Doubled arrows mean doubled current intensity.

In order to point out better the advantages and the features of the invention the known connections according to Figs. 1 and 2 are considered at first.

In Fig. 1, the eight strands distributed on the legs A and B are all series connected. In order to limit the stationary voltage difference between adjacent strands to four times the voltage of one strand the connections are so made that the first strand on leg A (terminals 0, 1) is connected to the second strand wound on leg B (terminals 1, 2), the latter in its turn to the third strand wound on leg A (terminals 2., '3) and lying to the right of the first strand. The fourth strand hes to the right of the second strand on leg B, the fifth to the left of the first strand on leg A. The sixth strand wound on leg B and lying to the left of the second strand is connected to the seventh strand lying to the right of the third strand on the leg A. Finally, the seventh-strand .is connected to the eighth strand wound on leg B and'lyingjto the right of the fourth strand. If the single strands were continually series connected, the voltage difference between two adjacent strands would be only twice the voltage of one step, but the voltage differencebetween the first and the seventh strand or the voltage difierence between the second and the eighth strand, which are six-times the voltage of one step, would appear betweenthe adjacent leads of two succeeding turns of the helix. -The terminals of each strand are led to the fixed contacts Eo-Eg of the ratio adjuster by the conductors F, the terminals of strands wound on leg B by using the series-connectors D. The conductor arrows H show the'direction of the circuits and which conductors carry current. It is evident, but may be noted, that the winding sections C, C, are wound in the samev sense as indicatedbyfthe arrows G. Independent of the number of the stages infservice only two conductors F are current-carrying... However, if heavy currents make necessary conductors of large crosssectional areas or if so high 'voltage'steps ,are provided that the usual conductor insulating would not be suflicient to withstand a voltage amounting to four times that of one step, the parallel connection as shown in Fig. 2 will be preferred. i 1

In Fig. 2, eight strands are wound on each leg A and B. The strands wound on ditferent legs are parallel connected in pairs by conductors D. The? series connection 'of the strands is made'by leads I from which the leads E branch ofi to the fixed contacts E -E of the selector switch. The stationary voltage difference between adjacent strands may be limited t'ci t'wo times the voltage of one stepbymaking the connections of the strands similar to Fig. 1. As indicated by the reference numerals the succession of the strands changes sothat the second strand will liet o the left of the first (on leg A) and the third strand to the right of the first, the fourth to the left of the second, the fifth to the right of the third, and so on. The winding sections C and C" have to be Wound in a different sense, as indicated by arrows G. The arrows H show also the direction of the currents and which conductors are current-carrying. It may be noted that if all steps are in service all leads I carry current. The leads I constitute a considerable part of the complete wiring in the transformer and their ohmic losses may affect the efficiency of the transformer. Furthermore, they must be braced by rigid clamping structures against forces due to short-circuit currents, which always involves difficulties or at least costs. Differences in the stray fields on the two legs affect the current division in the two parallel branches.

In order to overcome the disadvantages adhering to the above mentioned known regulating coils and yet to pre: serve the advantageous features of each we propose a new embodiment of said regulating coils and we de* scribe it with reference to Fig. 3. x v

In Fig. 3, A and B are the legs of a core type transformer. On each leg eight strands are wound in the manner of a helical coil. The strands of the two legs are series connected by leads D and each of said seriesconnecting leads D is lengthened to a contact point of the stage selector switch with its contacts E to E; by leads F. In Fig. 3, of the two parallel branches which result in this way one is shown in full lines and the other in broken lines. The winding sense of the two winding parts C, and C is the same as indicated by the arrows G. The terminals of each strand are, numbered 1 to 8. In order to show clearly which of them belong to one of the two parallel branches and which to the other, they bear the indices: and The-direction of the currents is indicated by arrows H. As shown in Fig. 3, the load current enters at contact E the regulating. coil and divides into two branches.

Branch one:

'E Strand 0"1 Strand 1"2" Strand 2"3 v0"1,) Strand 3"4 1II2II) Strand 4"5 V 2I!3II) Strand 5"6" 3II4II) Strand 6"7 Strand 7"8" 56")-E Branch two: 1

E -Strand 0'1 on leg B (to the left of 1n n) Strand 1'2 0n n) Strand 2'3 0'1)- Strand 3'4 1'2)- Strand 4'5 2'3)- Strand 5'6 y3'4!) Strand 6'7 on leg B (to the left of strand 45')- Strand 7'8 on leg A (to the left 0 The connection may be illustrated by a scheme lows:

on leg A on leg B on leg A (to the right of strand on leg B (to the right of on leg A (to the right of strand on leg B (to the right of strand on leg A (to the right of strand on leg B (to the right of strand strand on leg A (to the left of strand on leg B (to the left of strand on leg A (to the left of strand on leg B (to the left of strand on leg A (to the left of strand strand strand as folstrand Scheme 1 winding section 0 A winding section 0 (on leg-B) (on leg A) terminals of the I r i I! [I'll II I 1 I I u u n I! tran s glilg/ y firs/12? 513121;! illgl/ lg Terminals with thesame numerals and indices are to connect and to lead to the selector switch contacts.

Compared with the known connections according to Figs. 1 and 2 the following advantages will be notorious. At first, only the twofold voltage of a stage appears between adjacent strands in spite of the series connection of the strands; a feature which makes the series connection available also at high voltage steps without deterioration of the space factor by a reinforced strand insulation. On the other hand, the connection according to the invention involves all advantages of the parallel connection such as, for example, the subdivisibility of the conductor cross section that may be desirable in order to facilitate the manufacture of the coils, or to reduce the eddy currents in the conductors. These advantages are obtainable also by a connection according to Fig. 2 but there are also disadvantages which are avoided by a connection according to Fig. 3. 'First, in the embodiment shown by Fig. 2, all the leads which connect the terminals of the strands wound on the leg A (assuming all steps are in service) will have to carry the whole current (doubled arrows). Large copper cross sections are therefore necessary to keep sufficiently low the ohmic losses in these connecting leads. On. the contrary, by a connection according to our invention only two of said leads carry current (independent of the number of steps in service) andtheir current is only that of onestrand, that is only half the load current. Equal current densities supposed, it is obvious, that 50% ofthe copper may be saved with the connecting leads in question and, nevertheless, the ohmic losses are diminished. 'Furthermore, the currents in said leads run in opposite directions so that the ampere-turns are substantially compensated if the leads are laid sufficiently close together thereby reducing the induction of eddy currents in the neighboring metal parts, perhaps in the wall of the tank. The compensation of these ampere-turns is important also because the leads in question possess considerable inductance, especially when there are metal parts in the neighbor hood. Said inductance affects also the value of the short circuit voltage, of which an analytical computation will thus become dubious and will mean for the designer an uncertainty which by our invention is greatly reduced. A much greater advantage will, however, become evident by considering the forces acting on the leads in question in the event of a short circuit. As it is known, the forces between current conveying leads are proportional to the square of the ampere-turns, which means that (equal intensity of the load current and all stages in service supposed) the forces between the leads I or F in Fig. 2 are 8 :64 times the forces of the leads F in 3. This reduction of the dynamic forces acting on the leads makes possible. to use lighter clamping means. This and the aforementioned fact that eddy currents in neighboring metal parts are not to be feared, results, for obvious reasons, in a reduction of size, therewith also of weight and of costs of the whole regulating transformer.

As the strands on each leg are not only parallel con nected but also in series, small differences in the strayfields of the two legs do not affect the current distribution on the two parallel branches to the same extent as in the case of parallel connection, which. is important when each branch has its own selector switch.

Further two advantages of the connection according to this invention may still be set forth as suitable both for the producer and for the user. First, if the regulating coil or one part of it is to be substituted, the equal sense of winding of the two parts of the regulating coil makes said substitution easy. Secondly, all conductors (strands and all connecting leads to the selector switch) possess equal cross sections and allow thus of an easy manufacture and repair.

The connection according to this invention may also be used for regulating coils of shell type transformers. In such a case, the winding parts C C" form two concentric cylindrical coils surrounding the central leg. The winding parts C C" must of course be wound in a different winding sense. The connections have to be made as indicated in the above scheme. A disadvantage consisting in that the two concentric coils lie in different stray-fields, and disturbing the equal current-distribution on the two parallel branches when an odd number of steps are in service, may be avoided by a connection according to the following scheme:

Scheme 2 Because parallel connected strands, as itis seen'from the scheme, belong to the same winding section, they are also linked with the same stray-flux and the current division will be equal. The compensation of the ampereturns of the leads to the selector switch, however, is lost for all odd numbers of stages and the dynamic forces will be four times greater than those according to scheme (1), if the short circuit will take place with an even number of steps in service. The resulting ampere-turns, however, are only (assumed that seven stages are in service) two sevenths of the resulting ampere-turns in the case of a connection according to Fig. 2 and the dynamic forces (assumed that all stages are in service) are only one fourth.

Many variations of the connection according to our invention are possible. The following scheme may be Although our invention is described for a regulating coil with an even number of steps it is also applicable to a regulating-coil with an odd number of steps. For nine steps the scheme would be as follows:

Scheme 4 Winding section winding section 0 terminals Of the 17 1 11 /1 /1 1 1 u n u u n strands 8!6I4I2!0I 1/ 1/ 11 1 1 1 1 11 1311 11 1! The following connecting scheme is especially suitable if the two winding sections are arranged as concentric cylindrical coils: i l

6 Scheme Winding section (3 winding section 0 strands 11 11 11 11 1! terminals oi the The winding section C consisting of only eight strands may be composed of conductors of larger cross section so as to obtain the same length as the winding section C having ten strands.

Having now described our invention by means of some forms of its application we wish not to be limited in its scope by the following claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In combination in a regulating transformer, a coretype, single-phase transformer having legs, regulating windings comprising two winding parts respectively surrounding said legs of said transformer, each of said winding parts comprising a plurality of conductors extending adjacent one another in the direction of the axis of said core legs and being wound in a single layer in the manner of a helical coil, the number of said conductors of each winding part being equal to the number of regulating steps provided, connecting leads series-connecting the conductors of one winding part with the conductors of the other winding part, each of said series connecting leads being extended to a contact point of the stage selector switch, the movable contact of said stage selector switch connecting contact points having equal potential and connecting in parallel two winding-branches, each branch comprising a plurality of series-connected condoctors corresponding alternately to said two winding parts, said series connecting leads connecting said conductors so that the voltage difference between adjacent conductor turns of the two winding parts is only twofold of a voltage step.

2. In combination in a regulating transformer having a regulating winding comprising two winding parts surrounding as concentric cylindrical windings the central leg of a shell-type transformer, each winding part comprising a plurality of conductors extending adjacent one another in the direction of the axis of said central leg and being wound in a single layer in the manner of a helical coil, the number of said conductors of each winding part being equal to the number of regulating steps provided, connecting leads which series connect the conductors of one winding part with the conductors of the other winding part, each of said series connecting leads being extended to a contact point of the stage selector switch, the movable contact of said stage selector switch connecting contact points having equal potential and connecting in parallel in this way two winding branches each branch being composed of a plurality of series connected conductors corresponding alternately to said two winding parts, said series connecting leads connecting said conductors so that the voltage difference between adjacent conductor turns of two winding parts is only the two fold of a voltage step.

References Cited in the file of this patent UNITED STATES PATENTS 1,568,692 Pollock Ian. 5, 1926 2,757,347 Pozaryski July 31, 1956 FOREIGN PATENTS 23,366 Netherlands Jan. 15, 1931 481,233 Great Britain Mar. 8, 1938 

